Patent GB-911849-A (GB)
Title: Improvements in or relating to apparatus for measuring the coefficient of thermal conductivity of solid materials
Inventor: COGEZ PAUL
IPC: G01N25/18
Filed: 1960-04-14
Abstract: 911,849. Measuring thermal conductivity. COMMISSARIAT A L'ENERGIE ATOMIQUE. April 14, 1960 [April 15, 1959], No. 13407/60. Class 97 (3). The thermal conductivity of a specimen is evaluated by holding it resiliently between two reference specimens, one of which is heated, and measuring the thermal gradient along the chain so formed, the reference specimens (and the sample if so desired) being accurately centred in screens which have a thermal conductivity close to but not exceeding the particular specimen which they surround. The specimen 3 under test (Fig. 1) is held between the two reference specimens 2, 5 by means of spring-loaded members 1, 4, of which the latter is heated by an electric element 21 and the other is held at a definite temperature by the circulation of thermostatically controlled water. Loss of heat from the hot member 4 is minimised by holding this end of the frame against a ball 23 of refractory material which presses against an element 24 controlled by a screw 25 and spring 26. The specimens 2, 3, 5 are surrounded by removable screens 6, 7, 8 respectively which are of material such that their thermal conductivities are no greater than that of the corresponding specimen inside them. A suitable material for the screens, reference specimens and members 1 and 4 is soft iron containing less than 0.03% of carbon, sulphur and silicon. The whole assembly is held in two star-shaped supports 9, 10, the former of which has tubes 16, 17 to conduct the cooling water. These supports are linked by three rods (such as 11). carrying adjustable spring-loaded fingers. 29 for centering the assembly. This arrangement avoids errors due to differential expansion of the various units. The temperature gradient down the assembly is measured by eight thermocouples, 31-34 being on the surfaces of the reference specimens and 39-42 being on the surface of the sample. Further thermocouples are located on the outsides of the screens in positions corresponding to the others, and from the readings of all these the thermal conductivity of the sample can be calculated, knowing that of the reference specimens. The readings can be combined and fed to a recording or controlling potentiometer. The temperature gradient can be adjusted if necessary by auxiliary heating resistors inside the screens. The whole apparatus is surrounded by concentric glass tubes (Fig. 2, not shown) through which cooling water flows, and is mounted on a pillar which also contains a pump for creating a vacuum inside. The calibration of the apparatus can be checked by replacing the sample by a standard specimen, e.g. of pure metal. In a modification (Fig. 3) the thermocouple units 40-44 are replaced by refractory collars 56 fitted with refractory tubes 57, 58, 59 through which the thermocouples are passed; the auxiliary heaters 45 are also mounted in the collars. The tubes are slidable radially in holes in the collars and are arranged so that two of the thermocouples reach the specimen 3 while the third touches the surface of the screen, as shown in Fig. 5. Each thermocouple is mounted in a refractory sleeve 63, 65 which is bent through 90 degrees and urged towards the assembly by an adjustable blade spring 68. The latter can be retracted to allow the thermocouples to be removed. The thermocouple tubes 57, 58, 59 are lodged in recesses in the screen 7.